Eutectic bonding is a commonly used wafer bonding technique, which essentially involves bonding two eutectic metals to form a eutectic mixture. The fact that the two eutectic metals transform directly from solid to liquid state (or vice versa from liquid to solid state) at a specific composition and at a eutectic melting temperature, without passing a two-phase equilibrium, means that the eutectic melting temperature of the eutectic mixture can be much lower than the individual melting temperature of the two metals. This is advantageous as the bonding of the wafers can be achieved at a lower temperature which translates to lower wafer production costs.
However, the eutectic melting temperatures for most eutectic mixtures are still relatively high (more than 400° C.). Therefore, it is desirable to achieve bonding of wafers at temperatures even lower than the eutectic melting temperatures, so as to lower wafer production costs even further.
Furthermore, certain chips such as micro-electro mechanical systems (MEMS), light emitting diodes (LEDs) and bio-application devices could be temperature sensitive and exposure of these chips to high temperature conditions during bonding may result in defects. These defects include cracks of thin and fragile wafers, chip performance degradation, serious wafer/chip warpage and bonding quality degradation. Therefore, there is a need to devise a method for bonding wafers under temperature conditions even lower than the eutectic melting temperature.
Thus, what is required is a novel method for bonding wafers under low temperature conditions, or more specifically, temperature conditions below the eutectic melting temperature. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.